Am. J. Respir. Cell Mol. Biol.,
Volume 20, Number 3, March, 1999 517-529
Long-Lasting Effects of Chronic Ozone Exposure on Rat Nasal Epithelium
Jack R.
Harkema,
Jon A.
Hotchkiss,
Edward B.
Barr,
Catherine B.
Bennett,
Marianne
Gallup,
Jong Kwon
Lee,
and
Carol
Basbaum
Department of Pathology, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan; Lovelace
Respiratory Research Institute, Albuquerque, New Mexico; Department of Anatomy, University of California San Francisco,
San Francisco, California; and Division of Specific Toxicology, Toxicological Research Center, Korean Food and Drug
Administration, Seoul, Korea
Ozone, the principal oxidant pollutant in photochemical smog, causes airway epithelial injury in the upper
and lower respiratory tract of laboratory animals. We have recently reported that long-term inhalation exposure to ozone causes mucous-cell metaplasia (MCM) in the surface epithelium lining the nasal airways
of F344 rats. The principal objective of the present study was to determine the persistence of ozone-induced
MCM in the nasal epithelium after the end of a chronic exposure. Male F344/N rats were exposed to 0, 0.25, or 0.5 ppm ozone, for 8 h/d, 7 d/wk for 13 wk. Animals were killed 8 h, 4 wk, or 13 wk after the end
of the chronic exposure. Ozone-related alterations in the nasal epithelium were qualitatively and quantitatively characterized through histochemistry, image analysis, and morphometric techniques. Some rats
were exposed for an additional 8 h to 0.5 ppm ozone at 13 wk after the end of the chronic exposure to determine whether previous ozone exposure results in persistent changes in the sensitivity of nasal epithelium to acute injury. At the end of the chronic exposure, hyperplasia was present in the nasal epithelium of
rats exposed to 0.25 and 0.5 ppm ozone. By 13 wk postexposure, this proliferative alteration was still evident only in the rats exposed to 0.5 ppm ozone. Ozone-induced MCM with associated intraepithelial mucosubstances was evident only in the nasal tissues of rats exposed to 0.5 ppm ozone. Though attenuated,
these alterations in the nasal mucous apparatus were still detectable at 13 wk after the end of the exposure.
At this same time after the chronic exposure, an acute (8 h) exposure to 0.5 ppm ozone induced an additional increase of mucosubstances in the nasal epithelium of rats previously exposed to 0.5 ppm ozone, but
not in rats chronically exposed to 0 or 2.5 ppm ozone. The persistent nature of the ozone-induced MCM in
rats documented in this report suggests that ozone exposure may have the potential to induce similar long-lasting alterations in the airways of humans.
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Copyright © 1999 American Thoracic Society.
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